In the automation of screwing operations, especially in automobile and aircraft engineering, the highest quality standards have to be maintained and documented. For this the screwing tools employed are provided with inbuilt torque registering devices guaranteeing exact maintenance of the preadjusted maximum torques or angles of rotation.
For quality assurance the screwing tools powered pneumatically or electrically are tested at regular intervals on special test benches, after which each tool is given a test certificate.
With the testing equipment in general use the maximum cutout torques of the screwing tools are tested mainly, and readjusted if necessary. These testing devices function mostly on the basis of strain gauges or piezoelectrics, and are kept in special works proof test stations. They are based on values arrived at in the test laboratories through complicated measurements and calculations to define the relationship between the maximum tightening torque Mtot and the screw preload force FZ. To ensure an optimal non-positive connection these values must be determined for every screw connection.
The main purpose of the invention is to determine speedily and exactly the principal measured data of a new screw connection using a device according to the invention. For this it must be possible to measure separately the friction values of the screw head FRK on its contact surface and of the screw or nut in the thread FRG. This enables material pair values and lubricants to be optimized, so that repeatable screw preload forces FZ are obtained, while the unscrewing torques of screw locking deices can be determined and optimized. Important also is the ability to determine quickly and reliably three measured values
preload FZ 
head friction FRK 
thread friction FRG 
with different material pairs and surface states at different temperatures.
The invention makes possible a testing device consisting of a central measuring carrier part and interchangeable thread adapters and contact plates which can be screwed together in simple fashion.
Other objects, advantages and novel features of the present invention will become apparent from the following detail description of the invention when considered in conjunction with the accompanying drawings.